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What's with "tube amps"?

Guitarists typically consider tube amplifiers to be "better" than "solid state" amps. From the standpoint (of some level) of physics, what's the difference? What's the tube's function? How do they work? And does that explain the guitarists' preference?

They may prefer them because tube amps have different distortion patterns than solid state amps (note that solid state amps can be analogue, just as are tube amps): ""The sound of valves is inherently superior to that of any kind of semiconductor."
The "valve sound" is one phenomenon that may have a real existence; it has been known for a long time that listeners sometimes prefer to have a certain amount of second-harmonic distortion added in, [13] and most valve amplifiers provide just that, due to grave difficulties in providing good linearity with modest feedback factors. While this may well sound nice, hi-fi is supposedly about accuracy, and if the sound is to be thus modified it should be controllable from the front panel by a 'niceness' knob.
The use of valves leads to some intractable problems of linearity, reliability and the need for intimidatingly expensive (and once more, non-linear) iron-cored transformers. The current fashion is for exposed valves, and it is not at all clear to me that a fragile glass bottle, containing a red-hot anode with hundreds of volts DC on it, is wholly satisfactory for domestic safety." -- http://douglas-self.com/ampins/pseudo/subjectv.htm

Information about American English usage here and here. Floating point issues? Please read this before posting.

It's getting harder and harder to find an audio amp with less than 0.005% THD. Some even brag about 10% THD right on the box. (Home theatre, don't you know.)
But these weird tube things are getting ever more popular.
It may be that fewer and fewer companies make decent speakers anymore, so people literally cannot tell the distortion they're buying into.
-Fortunately contact cleaner fixed up my crudded up pots, and I don't have go wandering into what has become a totally alien world of modern stero amplifiers with a bit of quality for under $1000.
Sooner or later the capacitors will go, but maybe fashion will have changed by then.

In an earlier part of my life I tread a bit down the audiophile path. Not hardcore, never had the money for that. After much sampling I eventually settled on a pair of B&W DM640 speakers and a pair of B&K monobloc amps with a B&K pre-amp, which are solid state. This system sounded phenomenal, to me. Unlike many speakers of that time, and at the present I'd bet too, the DM640s are not overly bright, but rather very accurate, and therefore they don't destroy your hearing within 10 minutes.

I then spent some time searching for the best recordings of some of my favorite music. I had a good quality turntable / stylus and CD player (Maranzt CD63). What I discovered over time is that, in my experience / opinion, most all audiophile related claims are about as accurate as Gwyneth Paltrow's Goop products claims.

Speaker cables? simply buy some properly sized basic cable at radio shack. You won't be able to tell any difference between that and the $1000 cables.

Analog vinyl over digital CDs? A good quality recording and, if applicable, digital conversion is the key. I'll take a well done CD over vinyl any day. Virtually no human can tell the difference. Except that digital is much cheaper / easier to achieve clean play back. I almost never listen to any of the vinyl I still have and haven't for 25 years or more.

Tubes vs solid state? I challenge anyone to tell the difference between fine examples of both. Perhaps some people can do it reliably but I seriously doubt it. Solid state amps can do warmth and distortion just fine. One area in which tube amps arguably are better is in looks. I've seen very cool ones that look like they should be in an art museum. But who can afford them?

Tube vs solid state guitar amps? I don't really have any experience with this and don't play guitar. I'll take the artists' word on it. With a grain of salt.

The word "warmth" does not tell me what to listen for in the sound. I would have to hear side by side recordings that differ only in the amount of this warmth, and have someone walk me through it. For all I know it may be an attempt at describing a sensation that does not have an exact quantitative formula.

Some guitarists like a sound that a symphony orchestra listener would consider severely distorted.

I went through this back in the day i.e. in 1970. In those days transistor amps suffered from saturation which means a sudden spike in the signal caused a longer pulse of sound than it should and tube amps were much better in that one respect. Other issues such as the crossover error from plus to minus signal had been recently solved and there was plenty of power available from both types for the speakers although static types Quads were easier to drive with tubes at their higher voltages. The use of field effect transistors solved that saturation issue and now you will not be able to hear the difference, there have been blind tests, although audiophiles often claim to hear the difference. I was designing turntables back then and we knwew all the high frequencies were ripped out of vinyl the first time you played the disc, even with the best low force stylus hence the so called warm sound. My hearing and that of most people over, say 35 would not hear those high frequencies anyway, but my dog could.

sicut vis videre estoWhen we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.Originally Posted by Ken G

The word "warmth" does not tell me what to listen for in the sound. I would have to hear side by side recordings that differ only in the amount of this warmth, and have someone walk me through it. For all I know it may be an attempt at describing a sensation that does not have an exact quantitative formula.

Some guitarists like a sound that a symphony orchestra listener would consider severely distorted.

there was an interesting test on BBC a few months ago comparing analog and digital with self professed experts. the result was that increased volume was judged to be better quality in the tests and the experts were fooled by that simple variable. There is an interesting side issue regarding "attack" it is said that one can hear the attack for example in a struck piano string when the frequencies seen in that are higher than the audible range. There may be something in that. I have a special problem pushing sound through salt water and we use subjective tests. when we put a lot of bias on the very high frequencies, the attack was better especially on speech. You need to hear the consonants on speech to get clarity. It is at least possible the the brain can register those high frequencies through bone conduction even though we cannot hear a tone at those frequencies. It's an interesting area for hifi listening too because one of the differences in live music is the attack frequencies, so hard to get right with speakers. A speaker might give you a tone at say 12000 Hz, painful almost but it does not carry the attack sound of a piano or drum faithfully. Digital recording can also miss out but it might still be fanciful interpretation effects.

sicut vis videre estoWhen we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.Originally Posted by Ken G

This report seems to give the better technical aspects without too much detail. Tubes are more linear and don't have the clipping issues as much. The tubes for Ham radio transmitters when > 100 watts or so are, or were when I was active, called "linears". The TDH, mentioned earlier, is still a valid spec. to consider. Higher amperage has been the big problem in the past for solid state, which relates to guitar amps and powerful sound systems. The few good guitar players I know like tubes even in their pre-amp multi-effects boards.

When you get to high volumes class D amps are often used. These are pulsed output at high frequency and are more energy efficient. It's the same idea as used in high power DC motor control in essence. Most speaker types are still constructed like the old days but with clever long travel supports, so they integrate all those pulses to get back to analog sound waves. It's true that a single valve (sorry tube) is more linear than a single transistor or even a single op amp but the designs of amplifiers are quite clever and have been for years. That does not mean "cheap" systems have good THD figures unfortunately but they could have with a bit more effort. It's still true that a skilled listener can not really tell the difference between tube and transistor amplifiers (not counting overload distortion, that's hardly fair) but they will spot the difference between good and bad speakers. It's still true as it was in the 1950s that to get good fidelity, most money should go on the speakers, and the amp should be high powered, not because you want huge volume but the power is needed to push those attack sounds.
blind tests confirm those old ideas. Some of the best speakers I ever heard are not produced any more, I think, they were membranes with an array of conductors with strip magnets behind, rather like electrostatics but actually flat electrodynamic, very low impedance thus favouring transistor amplifiers. electrostatics favour tube amps. But they were large flat things and today we see those small tubes punching out the sound with long travel pistons. Years ago there was merit in tube amps for vinyl if only because of static hiss and pops, which was heard because the transistor preamps saturated. Today I think its nostalgia and why not? tubes are a great piece of technology.

sicut vis videre estoWhen we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.Originally Posted by Ken G

Years ago I read that in the 1960s, many international orchestras, in order to dispel accusations of racism. had auditioning musicians play behind a curtain. While it addressed visible minority issues, women also started winning positions. Top notch musicians had previously insisted men were better instrumentalists than women. Lol.

What sounds good is not necessarily what's the most "accurate". Subjective vs Objective.

Objectively speaking, it seems that upon sampling "accurate" speakers vs "bright" speakers, a significant majority of people choose the "bright" speakers. My personal experience is that they do sound better. For somewhere between 1 and 3 songs. Then they sound worse because your hearing can't take it anymore. It's similar to listening to overly loud music but without actually having the volume at what would typically be considered a loud setting.

The BBC test profloater mentioned at #11 above supports this. In a blind test of experts "the result was that increased volume was judged to be better quality in the tests and the experts were fooled by that simple variable."

Objectively speaking, it seems that upon sampling "accurate" speakers vs "bright" speakers, a significant majority of people choose the "bright" speakers. My personal experience is that they do sound better. For somewhere between 1 and 3 songs. Then they sound worse because your hearing can't take it anymore. It's similar to listening to overly loud music but without actually having the volume at what would typically be considered a loud setting.

The BBC test profloater mentioned at #11 above supports this. In a blind test of experts "the result was that increased volume was judged to be better quality in the tests and the experts were fooled by that simple variable."

A long time ago I worked for a while on new HiFi systems and we tested amps, vinyl turntables and speakers with a test panel. Most of the panel regarded themselves as music experts but were actually engineers. We did blind tests of our new speakers against pretty good commercial speakers, (I think they were Wharfdales), and it was obvious early on that volume improved perceived quality. One factor to consider is that high volume was somewhere near sitting in the front row with real instruments so that might be a genuine factor. Pushing the high frequencies up ie what we call brighter sound, also seemed to be perceived as better quality even when no longer true to the original. Unfortunately I cannot report whether this is an ageing factor, most people lose their high frequency hearing progressively and using a biased sound reproduction may be noticeable in a nostalgic way. instruments with low impact sounds such as violin family and wind are hard to distinguish between good and only moderate speakers but spoken voice and piano show up errors.

sicut vis videre estoWhen we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.Originally Posted by Ken G

My father once quoted a "golden ear" audiophile co-worker as saying "Too much bass" after hearing an orchestra in a concert hall for the first time. Apparently he was accustomed to some treble boost from his audio system, which could have included whatever was on the recordings.

On the topic of tubes versus solid state, I remember reading an article in one of the audio magazines decades ago. The author pointed out that it was not uncommon for a tube amplifier to have several per cent total harmonic distortion consisting almost entirely of second harmonic overtones, that is, and octave above the fundamental tone. That would audibly change the timbre of an instrument or a voice without introducing any harshness. Someone accustomed to that coloration might be dissatisfied with the more accurate reproduction of an amplifier with no distortion. A common problem with low budget transistor amps was crossover distortion in highly efficient bipolar designs which would have been impossible with tubes. This, along with hard clipping in the case of overloads, created high odd-numbered harmonics which had dreadfully harsh sound consequences even in very small amounts. These are faults that can be designed out of good solid state equipment.

One problem with product testing with some audiophiles is their rejection of double blind A-B testing by means of brief snippets. They argue that such testing does not adequately account for the nuances that go into great sound, and that only listening to complete performances over a long time on each device will tell them which device is more satisfying in the long run. Double blind comparison testing on these terms and conditions would be frightfully time consuming and expensive.